This invention relates to a process for reducing poisonous effects of metal contaminants such as iron, nickel, vanadium and the like, picked up by a hydrocarbon conversion catalyst during a hydrocarbon conversion process such as the high temperature conversion of a hydrocarbon feedstock containing such metals to a lower boiling product. More particularly, this invention relates to processes for reducing the poisonous effects of metal contaminants without removal of such contaminants from the catalyst, e.g., by a process of passivation.
During a catalyst promoted chemical conversion involving a hydrocarbon containing metal contaminants such as iron, nickel, and vanadium, the catalyst may become more and more deactivated due to the pick up of at least a portion of the metal poisons. Removal of such poisons from the catalyst may restore a substantial amount of the catalytic activity. However, no matter how carefully the process for removing the metal poisons from the catalyst is carried out, some penalty in the form of overall performance is often paid. Accordingly, a simple and straight forward method for overcoming the deleterious effects of the metal poisons or contaminants is desirable.
U.S. Pat. No. 3,324,044 (1967) discloses a method for restoring the catalytic activity of silica-alumina catalysts that are contaminated with metals such as iron, nickel and vanadium. The method involves removal of metal-contaminants from such catalysts by treating them at a temperature of at least 150.degree. F. for at least 30 minutes with diluted aqueous solutions, which contain not more than 5% by weight of a water-soluble acidic aluminum salt and have a pH of from 2.0 to 5.5
Catalytically promoted methods for the chemical conversion of hydrocarbons include cracking, hydrocracking, reforming, hydrodenitrogenation, hydrodesulfurization, etc. Such reactions generally are performed at elevated temperatures, for example, about 300.degree. to 1200.degree. F., more often 600.degree. to 1000.degree. F. Feedstocks to these processes comprise normally liquid or solid hydrocarbons which, at the temperature of the conversion reaction, are generally in a fluid, i.e., liquid or vapor, state and the products of the conversion usually are more valuable, lower boiling materials.
Although referred to as "metals", these catalyst contaminants may be present in the hydrocarbon feed in the form of free metals or relatively non-volatile metal compounds. It is, therefore, to be understood that the term "metal" as used herein refers to either form. Various petroleum stocks have been known to contain at least traces of many metals. For example, Middle Eastern crudes contain relatively high amounts of several metal components, while Venezuelan crudes are noteworthy for their vanadium content and are relatively low in other contaminating metals such as nickel. In addition to metals naturally present in petroleum stocks, including some iron, petroleum stocks also have a tendency to pick up tramp iron from transportation, storage and processing equipment. Most of these metals, when present in a stock, deposit in a relatively non-volatile form on the catalyst during conversion processes so that regeneration of the catalyst to remove deposited coke does not also remove these contaminants. With the increased importance of gasoline in the world today and the shortages of crude oils and increased prices, it is becoming more and more important to process any type or portions of a crude source, including those highly metal contaminated crudes to more valuable products.
Of the various metals which are to be found in representative hydrocarbon feedstocks some, like the alkali metals, only deactivate the catalyst without changing the product distribution; therefore, they might be considered true poisons. Others such as iron, nickel, vanadium, and copper markedly alter the selectivity and activity of cracking reactions if allowed to accumulate on the catalyst and, since they affect process performance, they are also referred to as "poisons". A poisoned catalyst with these metals generally produces a higher yield of coke and hydrogen at the expense of desired products, such as gasoline and butanes. For instance, U.S. Pat. No. 3,147,228 reports that it has been shown that the yield of butanes, butenes and gasoline, based on converting 60 volume percent of cracking feed to lighter materials and coke dropped from 58.5 to 49.6 volume percent when the amount of nickel on the catalyst increased from 55 ppm to 645 ppm and the amount of vanadium increased from 145 ppm to 1480 ppm in a fluid catalytic cracking of a feedstock containing some metal contaminated stocks. Since many cracking units are limited by coke burning or gas handling facilities, increased coke or gas yields require a reduction in conversion or throughput to stay within the unit capacity.
The present invention is particularly suitable for passivating poisons in a catalyst utilized in the catalytic cracking of reduced or topped crude oils to more valuable products such as illustrated in U.S. Pat. Nos. 3,092,568 and 3,164,542. The teachings of which are incorporated by reference herein. Similarly, this invention is applicable to processing shale oils, tar sands oil, coal oils and the like where metal contamination of the processing, e.g., cracking, catalyst can occur.